There are multiple reasons for volume spikes and you can classify them broadly into two buckets: informed volume vs. liquidity driven volume.
Informed volume is price sensitive and happens when you buy and sell because of new information about the stock or market. E.g. the company is doing much better than you expected or vice versa. Earnings events drive informed volume. Company specific events (or market events like FOMC) also drive informed volume.
Liquidity driven volume is not price sensitive and happens when you buy and sell for cash or to use cash. For example, every time you get your payroll and a % goes into the market, there is incremental buying/selling. Rebalancing activities, option positioning, and time-of-the-year effects (seasonality) explain those.
So using a volume filter is not helpful because you still need to classify what type of volume is occurring.
The who is buying part... most professionals think that the marginal buyer of stocks are long only investors like wealth managers and mutual fund managers. Since those types of investors aren't focused on predicting quarterly earnings, and prefer to take a longer term view, they will be the biggest incremental buyer or seller. Hedge funds and other speculators are buying before (and also after depending on the results).
